1. Field of the Invention
The present invention relates to a semiconductor memory device and a method of manufacturing the same.
2. Background Art
A demand for an NOR flash memory as a semiconductor memory device for digital cameras, portable telephones, and portable audio devices is increasing rapidly. These devices are increasingly required to have a smaller size, a lighter weight, and an advanced function. Along these trends, miniaturization, high integration, a low power supply voltage, and improved reliability are required for the NOR flash memory.
However, when the power supply voltage is reduced, operating speed of the NOR flash memory decreases. When the power supply voltage is increased, the operating speed improves, but the requirement for the low power supply voltage cannot be satisfied.
When memory cells are miniaturized, electric charges cannot be stored sufficiently in a floating gate electrode, and a threshold voltage of the memory cells decreases. This reduces reliability.